The present invention relates in general to the field of hologram production and, more particularly, hologram production using light field rendering techniques.
Traditionally, the input to a three dimensional (3D) graphics system is a scene comprising geometric primitives composed of different materials and virtually illuminated by one or more light sources. Based on this input specification, a computer graphics rendering system computes and outputs an image. In recent years, a new approach to computer graphics rendering has emerged, namely imaged-based rendering. Image-based rendering systems typically generate different views of an environment from a set of pre-acquired imagery.
The development of image-based rendering techniques generally, and the application of those techniques to the field of holography have inspired the development of light field rendering as described by, for example, M. Levoy and P. Hanrahan in xe2x80x9cLight Field Rendering,xe2x80x9d in Proceedings of SIGGRAPH ""96, (New Orleans, La., Aug. 4-9, 1996), and in Computer Graphics Proceedings, Annual Conference Series, pages 31-42, ACM SIGGRAPH, 1996, which are hereby incorporated by reference herein in their entirety. The light field represents the amount of light passing through all points in 3D space along all possible directions. It can be represented by a high-dimensional function giving radiance as a function of time, wavelength, position and direction. The light field is relevant to image-based models because images are two-dimensional projections of the light field. Images can then be viewed as xe2x80x9cslicesxe2x80x9d cut through the light field. Additionally, one can construct higher-dimensional computer-base models of the light field using images. A given model can also be used to extract and synthesize new images different from those used to build the model.
Formally, the light field represents the radiance flowing through all the points in a scene in all possible directions. For a given wavelength, one can represent a static light field as a five-dimensional (5D) scalar function L(x, y, z, xcex8, xcfx86) that gives radiance as a function of location (x, y, z) in 3D space and the direction (xcex8, xcfx86) the light is traveling. Note that this definition is equivalent to the definition of plenoptic function. Typical discrete (i.e., those implemented in real computer systems) light-field models represent radiance as a red, green and blue triple, and consider static time-independent light-field data only, thus reducing the dimensionality of the light-field function to five dimensions and three color components. Modeling the light-field thus requires processing and storing a 5D function whose support is the set of all rays in 3D Cartesian space. However, light field models in computer graphics usually restrict the support of the light-field function to four-dimensional (4D) oriented line space. Two types of 4D light-field representations have been proposed, those based on planar parameterizations and those based on spherical, or isotropic, parameterizations.
The light-field representations based on planar parameterizations were inspired by classic computer graphics planar projections and by traditional two-step holography. For example, the two-plane parameterization (2PP) represents each oriented line in the 4D oriented line space by its intersection points with two ordered planes, a front plane (s, t) and a back plane (u, v), as illustrated in FIG. 1. The front and back planes together form a xe2x80x9clight slab.xe2x80x9d FIG. 1 illustrates the 2D analogy of the geometry involved in rendering a 2PP-based light-field representation. C is the center of projection, S is a spherical projection surface, dAS is a differential area on S, P is the projection plane, dAp is a differential area on P, D is the distance between C and the front plane of parameterization, xcex2 is the angle at which the differential pencil dl intersects that plane, and d is the (constant) orthogonal distance between the two planes.
Rendering algorithms to generate and build 2PP-based light fields have been proposed in the context of computer-generated holography and particularly holographic stereogramns, including the work described in the aforementioned paper by Levoy and Hanrahan. Holographic stereograms are discrete computer-generated holograms that optically store light-field discretetization via optical interference patterns recorded in a holographic recording material.
The choice of 2PP parameterization is primarily inspired by traditional two-step holography. The choice also simplifies rendering by avoiding the use of cylindrical and spherical projections during the light-field reconstruction process However, 2PP does not provide a uniform sampling of 3D line space. Moreover, even those 2PP models that rely on uniform samplings of the planes are known to introduce biases in the line sampling densities of the light field. Those biases are intrinsic to the parameterization and cannot be eliminated by increasing the number of slabs or changing the planes relative positions and orientations. Additionally, algorithms designed to enhance the speed with which computer graphics rendering is performed in the 2PP context, such as the algorithms described in M. Halle and A. Kropp, xe2x80x9cFast Computer Graphics Rendering for Full Parallax Spatial Displays,xe2x80x9d Practical Holography XI, Proc. SPIE, vol. 3011, pages 105-112, Feb. 10-11, 1997, which is hereby incorporated by reference herein in its entirety, often introduce additional (and undesirable) rendering artifacts and are susceptible to problems associated with anti-aliasing.
Accordingly, it is desirable to use light-field rendering techniques in hologram production while reducing or eliminating some or all of the problems associated with light-field rendering using 2PP light fields.
It has been discovered that using an isotropic, direction and point parameterization (DPP) light-field model for rendering can provide advantages in hologram production including reduced image artifacts, reduced oversampling, decreased rendering time, and decreased data storage requirements.
Accordingly, one aspect of the present invention provides a computer-implemented method of generating data for producing a hologram. A computer graphics model of a scene is provided. A first set of light-field data and a second set of light-field data are generated from the computer graphics model of a scene using an isotropic parameterization of a light field. Data from the first set of light-field data and the second set of light-field data are combined to produce at least one hogel image.
The foregoing is a summary and thus contains, by necessity, simplifications, generalizations and omissions of detail; consequently, those skilled in the art will appreciate that the summary is illustrative only and is not intended to be in any way limiting. As will also be apparent to one of skill in the art, the operations disclosed herein may be implemented in a number of ways, and such changes and modifications may be made without departing from this invention and its broader aspects. Other aspects, inventive features, and advantages of the present invention, as defined solely by the claims, will become apparent in the non-limiting detailed description set forth below.